text: (function() {
  
    var supportCustomEvent = window.CustomEvent;
    if (!supportCustomEvent || typeof supportCustomEvent == 'object') {
      supportCustomEvent = function CustomEvent(event, x) {
        x = x || {};
        var ev = document.createEvent('CustomEvent');
        ev.initCustomEvent(event, !!x.bubbles, !!x.cancelable, x.detail || null);
        return ev;
      };
      supportCustomEvent.prototype = window.Event.prototype;
    }
  
    /**
     * Finds the nearest <dialog> from the passed element.
     *
     * @param {Element} el to search from
     * @return {HTMLDialogElement} dialog found
     */
    function findNearestDialog(el) {
      while (el) {
        if (el.nodeName.toUpperCase() == 'DIALOG') {
          return /** @type {HTMLDialogElement} */ (el);
        }
        el = el.parentElement;
      }
      return null;
    }
  
    /**
     * Blur the specified element, as long as it's not the HTML body element.
     * This works around an IE9/10 bug - blurring the body causes Windows to
     * blur the whole application.
     *
     * @param {Element} el to blur
     */
    function safeBlur(el) {
      if (el && el.blur && el != document.body) {
        el.blur();
      }
    }
  
    /**
     * @param {!NodeList} nodeList to search
     * @param {Node} node to find
     * @return {boolean} whether node is inside nodeList
     */
    function inNodeList(nodeList, node) {
      for (var i = 0; i < nodeList.length; ++i) {
        if (nodeList[i] == node) {
          return true;
        }
      }
      return false;
    }
  
    /**
     * @param {!HTMLDialogElement} dialog to upgrade
     * @constructor
     */
    function dialogPolyfillInfo(dialog) {
      this.dialog_ = dialog;
      this.replacedStyleTop_ = false;
      this.openAsModal_ = false;
  
      // Set a11y role. Browsers that support dialog implicitly know this already.
      if (!dialog.hasAttribute('role')) {
        dialog.setAttribute('role', 'dialog');
      }
  
      dialog.show = this.show.bind(this);
      dialog.showModal = this.showModal.bind(this);
      dialog.close = this.close.bind(this);
  
      if (!('returnValue' in dialog)) {
        dialog.returnValue = '';
      }
  
      this.maybeHideModal = this.maybeHideModal.bind(this);
      if ('MutationObserver' in window) {
        // IE11+, most other browsers.
        var mo = new MutationObserver(this.maybeHideModal);
        mo.observe(dialog, { attributes: true, attributeFilter: ['open'] });
      } else {
        dialog.addEventListener('DOMAttrModified', this.maybeHideModal);
      }
      // Note that the DOM is observed inside DialogManager while any dialog
      // is being displayed as a modal, to catch modal removal from the DOM.
  
      Object.defineProperty(dialog, 'open', {
        set: this.setOpen.bind(this),
        get: dialog.hasAttribute.bind(dialog, 'open')
      });
  
      this.backdrop_ = document.createElement('div');
      this.backdrop_.className = 'backdrop';
      this.backdropClick_ = this.backdropClick_.bind(this);
    }
  
    dialogPolyfillInfo.prototype = {
  
      get dialog() {
        return this.dialog_;
      },
  
      /**
       * Maybe remove this dialog from the modal top layer. This is called when
       * a modal dialog may no longer be tenable, e.g., when the dialog is no
       * longer open or is no longer part of the DOM.
       */
      maybeHideModal: function() {
        if (!this.openAsModal_) { return; }
        if (this.dialog_.hasAttribute('open') &&
            document.body.contains(this.dialog_)) { return; }
  
        this.openAsModal_ = false;
        this.dialog_.style.zIndex = '';
  
        // This won't match the native <dialog> exactly because if the user set
        // top on a centered polyfill dialog, that top gets thrown away when the
        // dialog is closed. Not sure it's possible to polyfill this perfectly.
        if (this.replacedStyleTop_) {
          this.dialog_.style.top = '';
          this.replacedStyleTop_ = false;
        }
  
        // Optimistically clear the modal part of this <dialog>.
        this.backdrop_.removeEventListener('click', this.backdropClick_);
        if (this.backdrop_.parentElement) {
          this.backdrop_.parentElement.removeChild(this.backdrop_);
        }
        dialogPolyfill.dm.removeDialog(this);
      },
  
      /**
       * @param {boolean} value whether to open or close this dialog
       */
      setOpen: function(value) {
        if (value) {
          this.dialog_.hasAttribute('open') || this.dialog_.setAttribute('open', '');
        } else {
          this.dialog_.removeAttribute('open');
          this.maybeHideModal();  // nb. redundant with MutationObserver
        }
      },
  
      /**
       * Handles clicks on the fake .backdrop element, redirecting them as if
       * they were on the dialog itself.
       *
       * @param {!Event} e to redirect
       */
      backdropClick_: function(e) {
        var redirectedEvent = document.createEvent('MouseEvents');
        redirectedEvent.initMouseEvent(e.type, e.bubbles, e.cancelable, window,
            e.detail, e.screenX, e.screenY, e.clientX, e.clientY, e.ctrlKey,
            e.altKey, e.shiftKey, e.metaKey, e.button, e.relatedTarget);
        this.dialog_.dispatchEvent(redirectedEvent);
        e.stopPropagation();
      },
  
      /**
       * Focuses on the first focusable element within the dialog. This will always blur the current
       * focus, even if nothing within the dialog is found.
       */
      focus_: function() {
        // Find element with `autofocus` attribute, or fall back to the first form/tabindex control.
        var target = this.dialog_.querySelector('[autofocus]:not([disabled])');
        if (!target) {
          // Note that this is 'any focusable area'. This list is probably not exhaustive, but the
          // alternative involves stepping through and trying to focus everything.
          var opts = ['button', 'input', 'keygen', 'select', 'textarea'];
          var query = opts.map(function(el) {
            return el + ':not([disabled])';
          });
          // TODO(samthor): tabindex values that are not numeric are not focusable.
          query.push('[tabindex]:not([disabled]):not([tabindex=""])');  // tabindex != "", not disabled
          target = this.dialog_.querySelector(query.join(', '));
        }
        safeBlur(document.activeElement);
        target && target.focus();
      },
  
      /**
       * Sets the zIndex for the backdrop and dialog.
       *
       * @param {number} backdropZ
       * @param {number} dialogZ
       */
      updateZIndex: function(backdropZ, dialogZ) {
        this.backdrop_.style.zIndex = backdropZ;
        this.dialog_.style.zIndex = dialogZ;
      },
  
      /**
       * Shows the dialog. If the dialog is already open, this does nothing.
       */
      show: function() {
        if (!this.dialog_.open) {
          this.setOpen(true);
          this.focus_();
        }
      },
  
      /**
       * Show this dialog modally.
       */
      showModal: function() {
        if (this.dialog_.hasAttribute('open')) {
          throw new Error('Failed to execute \'showModal\' on dialog: The element is already open, and therefore cannot be opened modally.');
        }
        if (!document.body.contains(this.dialog_)) {
          throw new Error('Failed to execute \'showModal\' on dialog: The element is not in a Document.');
        }
        if (!dialogPolyfill.dm.pushDialog(this)) {
          throw new Error('Failed to execute \'showModal\' on dialog: There are too many open modal dialogs.');
        }
        this.show();
        this.openAsModal_ = true;
  
        // Optionally center vertically, relative to the current viewport.
        if (dialogPolyfill.needsCentering(this.dialog_)) {
          dialogPolyfill.reposition(this.dialog_);
          this.replacedStyleTop_ = true;
        } else {
          this.replacedStyleTop_ = false;
        }
  
        // Insert backdrop.
        this.backdrop_.addEventListener('click', this.backdropClick_);
        this.dialog_.parentNode.insertBefore(this.backdrop_,
            this.dialog_.nextSibling);
      },
  
      /**
       * Closes this HTMLDialogElement. This is optional vs clearing the open
       * attribute, however this fires a 'close' event.
       *
       * @param {string=} opt_returnValue to use as the returnValue
       */
      close: function(opt_returnValue) {
        if (!this.dialog_.hasAttribute('open')) {
          throw new Error('Failed to execute \'close\' on dialog: The element does not have an \'open\' attribute, and therefore cannot be closed.');
        }
        this.setOpen(false);
  
        // Leave returnValue untouched in case it was set directly on the element
        if (opt_returnValue !== undefined) {
          this.dialog_.returnValue = opt_returnValue;
        }
  
        // Triggering "close" event for any attached listeners on the <dialog>.
        var closeEvent = new supportCustomEvent('close', {
          bubbles: false,
          cancelable: false
        });
        this.dialog_.dispatchEvent(closeEvent);
      }
  
    };
  
    var dialogPolyfill = {};
  
    dialogPolyfill.reposition = function(element) {
      var scrollTop = document.body.scrollTop || document.documentElement.scrollTop;
      var topValue = scrollTop + (window.innerHeight - element.offsetHeight) / 2;
      element.style.top = Math.max(scrollTop, topValue) + 'px';
    };
  
    dialogPolyfill.isInlinePositionSetByStylesheet = function(element) {
      for (var i = 0; i < document.styleSheets.length; ++i) {
        var styleSheet = document.styleSheets[i];
        var cssRules = null;
        // Some browsers throw on cssRules.
        try {
          cssRules = styleSheet.cssRules;
        } catch (e) {}
        if (!cssRules)
          continue;
        for (var j = 0; j < cssRules.length; ++j) {
          var rule = cssRules[j];
          var selectedNodes = null;
          // Ignore errors on invalid selector texts.
          try {
            selectedNodes = document.querySelectorAll(rule.selectorText);
          } catch(e) {}
          if (!selectedNodes || !inNodeList(selectedNodes, element))
            continue;
          var cssTop = rule.style.getPropertyValue('top');
          var cssBottom = rule.style.getPropertyValue('bottom');
          if ((cssTop && cssTop != 'auto') || (cssBottom && cssBottom != 'auto'))
            return true;
        }
      }
      return false;
    };
  
    dialogPolyfill.needsCentering = function(dialog) {
      var computedStyle = window.getComputedStyle(dialog);
      if (computedStyle.position != 'absolute') {
        return false;
      }
  
      // We must determine whether the top/bottom specified value is non-auto.  In
      // WebKit/Blink, checking computedStyle.top == 'auto' is sufficient, but
      // Firefox returns the used value. So we do this crazy thing instead: check
      // the inline style and then go through CSS rules.
      if ((dialog.style.top != 'auto' && dialog.style.top != '') ||
          (dialog.style.bottom != 'auto' && dialog.style.bottom != ''))
        return false;
      return !dialogPolyfill.isInlinePositionSetByStylesheet(dialog);
    };
  
    /**
     * @param {!Element} element to force upgrade
     */
    dialogPolyfill.forceRegisterDialog = function(element) {
      if (element.showModal) {
        console.warn('This browser already supports <dialog>, the polyfill ' +
            'may not work correctly', element);
      }
      if (element.nodeName.toUpperCase() != 'DIALOG') {
        throw new Error('Failed to register dialog: The element is not a dialog.');
      }
      new dialogPolyfillInfo(/** @type {!HTMLDialogElement} */ (element));
    };
  
    /**
     * @param {!Element} element to upgrade
     */
    dialogPolyfill.registerDialog = function(element) {
      if (element.showModal) {
        console.warn('Can\'t upgrade <dialog>: already supported', element);
      } else {
        dialogPolyfill.forceRegisterDialog(element);
      }
    };
  
    /**
     * @constructor
     */
    dialogPolyfill.DialogManager = function() {
      /** @type {!Array<!dialogPolyfillInfo>} */
      this.pendingDialogStack = [];
  
      // The overlay is used to simulate how a modal dialog blocks the document.
      // The blocking dialog is positioned on top of the overlay, and the rest of
      // the dialogs on the pending dialog stack are positioned below it. In the
      // actual implementation, the modal dialog stacking is controlled by the
      // top layer, where z-index has no effect.
      this.overlay = document.createElement('div');
      this.overlay.className = '_dialog_overlay';
      this.overlay.addEventListener('click', function(e) {
        e.stopPropagation();
      });
  
      this.handleKey_ = this.handleKey_.bind(this);
      this.handleFocus_ = this.handleFocus_.bind(this);
      this.handleRemove_ = this.handleRemove_.bind(this);
  
      this.zIndexLow_ = 100000;
      this.zIndexHigh_ = 100000 + 150;
    };
  
    /**
     * @return {Element} the top HTML dialog element, if any
     */
    dialogPolyfill.DialogManager.prototype.topDialogElement = function() {
      if (this.pendingDialogStack.length) {
        var t = this.pendingDialogStack[this.pendingDialogStack.length - 1];
        return t.dialog;
      }
      return null;
    };
  
    /**
     * Called on the first modal dialog being shown. Adds the overlay and related
     * handlers.
     */
    dialogPolyfill.DialogManager.prototype.blockDocument = function() {
      document.body.appendChild(this.overlay);
      document.body.addEventListener('focus', this.handleFocus_, true);
      document.addEventListener('keydown', this.handleKey_);
      document.addEventListener('DOMNodeRemoved', this.handleRemove_);
    };
  
    /**
     * Called on the first modal dialog being removed, i.e., when no more modal
     * dialogs are visible.
     */
    dialogPolyfill.DialogManager.prototype.unblockDocument = function() {
      document.body.removeChild(this.overlay);
      document.body.removeEventListener('focus', this.handleFocus_, true);
      document.removeEventListener('keydown', this.handleKey_);
      document.removeEventListener('DOMNodeRemoved', this.handleRemove_);
    };
  
    dialogPolyfill.DialogManager.prototype.updateStacking = function() {
      var zIndex = this.zIndexLow_;
  
      for (var i = 0; i < this.pendingDialogStack.length; i++) {
        if (i == this.pendingDialogStack.length - 1) {
          this.overlay.style.zIndex = zIndex++;
        }
        this.pendingDialogStack[i].updateZIndex(zIndex++, zIndex++);
      }
    };
  
    dialogPolyfill.DialogManager.prototype.handleFocus_ = function(event) {
      var candidate = findNearestDialog(/** @type {Element} */ (event.target));
      if (candidate != this.topDialogElement()) {
        event.preventDefault();
        event.stopPropagation();
        safeBlur(/** @type {Element} */ (event.target));
        // TODO: Focus on the browser chrome (aka document) or the dialog itself
        // depending on the tab direction.
        return false;
      }
    };
  
    dialogPolyfill.DialogManager.prototype.handleKey_ = function(event) {
      if (event.keyCode == 27) {
        event.preventDefault();
        event.stopPropagation();
        var cancelEvent = new supportCustomEvent('cancel', {
          bubbles: false,
          cancelable: true
        });
        var dialog = this.topDialogElement();
        if (dialog.dispatchEvent(cancelEvent)) {
          dialog.close();
        }
      }
    };
  
    dialogPolyfill.DialogManager.prototype.handleRemove_ = function(event) {
      if (event.target.nodeName.toUpperCase() != 'DIALOG') { return; }
  
      var dialog = /** @type {HTMLDialogElement} */ (event.target);
      if (!dialog.open) { return; }
  
      // Find a dialogPolyfillInfo which matches the removed <dialog>.
      this.pendingDialogStack.some(function(dpi) {
        if (dpi.dialog == dialog) {
          // This call will clear the dialogPolyfillInfo on this DialogManager
          // as a side effect.
          dpi.maybeHideModal();
          return true;
        }
      });
    };
  
    /**
     * @param {!dialogPolyfillInfo} dpi
     * @return {boolean} whether the dialog was allowed
     */
    dialogPolyfill.DialogManager.prototype.pushDialog = function(dpi) {
      var allowed = (this.zIndexHigh_ - this.zIndexLow_) / 2 - 1;
      if (this.pendingDialogStack.length >= allowed) {
        return false;
      }
      this.pendingDialogStack.push(dpi);
      if (this.pendingDialogStack.length == 1) {
        this.blockDocument();
      }
      this.updateStacking();
      return true;
    };
  
    /**
     * @param {dialogPolyfillInfo} dpi
     */
    dialogPolyfill.DialogManager.prototype.removeDialog = function(dpi) {
      var index = this.pendingDialogStack.indexOf(dpi);
      if (index == -1) { return; }
  
      this.pendingDialogStack.splice(index, 1);
      this.updateStacking();
      if (this.pendingDialogStack.length == 0) {
        this.unblockDocument();
      }
    };
  
    dialogPolyfill.dm = new dialogPolyfill.DialogManager();
  
    /**
     * Global form 'dialog' method handler. Closes a dialog correctly on submit
     * and possibly sets its return value.
     */
    document.addEventListener('submit', function(ev) {
      var target = ev.target;
      if (!target || !target.hasAttribute('method')) { return; }
      if (target.getAttribute('method').toLowerCase() != 'dialog') { return; }
      ev.preventDefault();
  
      var dialog = findNearestDialog(/** @type {Element} */ (ev.target));
      if (!dialog) { return; }
  
      // FIXME: The original event doesn't contain the element used to submit the
      // form (if any). Look in some possible places.
      var returnValue;
      var cands = [document.activeElement, ev.explicitOriginalTarget];
      var els = ['BUTTON', 'INPUT'];
      cands.some(function(cand) {
        if (cand && cand.form == ev.target && els.indexOf(cand.nodeName.toUpperCase()) != -1) {
          returnValue = cand.value;
          return true;
        }
      });
      dialog.close(returnValue);
    }, true);
  
    dialogPolyfill['forceRegisterDialog'] = dialogPolyfill.forceRegisterDialog;
    dialogPolyfill['registerDialog'] = dialogPolyfill.registerDialog;
  
    if (typeof module === 'object' && typeof module['exports'] === 'object') {
      // CommonJS support
      module['exports'] = dialogPolyfill;
    } else if (typeof define === 'function' && 'amd' in define) {
      // AMD support
      define(function() { return dialogPolyfill; });
    } else {
      // all others
      window['dialogPolyfill'] = dialogPolyfill;
    }
  })();
  